1. Field of Invention
The present invention relates to an electroluminescent display, and a controller for controlling the intensity and operation of the electroluminescent (EL) display.
2. Description of Related Art
Traditional drive techniques for EL displays include high frequency sinusoidal alternating current (AC) or high voltage square pulses. The AC approach uses voltages between 80 and 135 Volts rms and frequencies between 800 and 1200 Hz. Unfortunately, this method offers only basic illumination without independent adjustment of intensity, e.g., between channels of an electroluminescent display. The alternating high voltage square pulse technique provides sophisticated control of the display but exposes the display to transients that may reduce its usable life.
An example of a control circuit can be found in U.S. Pat. No. 6,043,609 issued to George et al. The control circuit in this device includes a switch that is turned on and off so as to maintain a constant current level and frequency of the drive signal to the electroluminescent lamp substantially over its operating life. The voltage applied is allowed to increase to a predetermined limiting value in order to provide compensation due to aging of the lamp. However, George et al. does not address controlling intensity of individual channels or elements of an electroluminescent display.
Other prior art control circuits are disclosed in U.S. Pat. Nos. 5,814,947 and 5,293,098 issued to Brownell. These control circuits use an inverter to apply a full sinusoidal waveform to the electroluminescent display. Brownell accommodates switching on/off display elements by adjusting a base frequency based on the impedance of the lamp. However, adjusting base frequency disadvantageously shortens the display life and does not provide as significant an increase in illumination intensity as does an amplitude correction. Brownell does not address controlling intensity of individual display channels or elements of an electroluminescent display.
Yet another prior art control implementation is disclosed in U.S. Pat. No. 4,845,489 issued to Hormel. This control circuit compensates for the decrease in capacitance of an EL display by using an RC time constant which effectively increases the voltage presented across the EL display. Unfortunately, voltage increases generally must be applied across an entire EL display. Another disadvantage with direct voltage corrections is that once voltage has been increased to a maximum point, no further adjustment can be provided. Hormel does not control the intensity of individual channels or elements of an electroluminescent display.
In view of the foregoing, there is a need in the art for a controller for an EL display capable of adjusting the intensity of individual display channels or elements without disadvantageously shortening the life of the EL display. Additionally, there is a need for an EL controller which adjusts the intensity of individual channels or elements to individually compensate for lamp aging, color filters, and eye sensitivity to the color spectrum.
The present invention comprises an electroluminescent display and controller for controlling the intensity of individual channels or elements of the electroluminescent display. The controller may be configured to control each channel or element of the electroluminescent display independent of the other display elements.
The electroluminescent display comprises a plurality of display elements (or channels), each having a first electrode and a second or common (shared) electrode, although the present invention is equally suitable for use with a display having a single display element. According to one embodiment of the invention, the display is used on a gaming device or a gaming apparatus, although the present invention may be used for any suitable application or device incorporating an electroluminescent display.
The means for controlling the intensity of each display element independent of other display elements comprises an EL controller. According to one illustrative embodiment, the controller comprises a processor, a half-wave waveform generator controlled by the processor, and a drive circuit controlled by the processor, that alternately applies the half-wave waveform to the first electrode and connects the second electrode to ground; and alternately applies the half-wave waveform to the second electrode and connects the first electrode to ground. Illumination of a display element occurs when the first and second electrode are xe2x80x9cout of phasexe2x80x9d as described in more detail below. Conversely, a display element is not illuminated when the first and second electrodes xe2x80x9care in phasexe2x80x9d.
The waveform generator provides a waveform to each element of the electroluminescent display as driven by the drive circuit and as dictated by the controller. In particular, the processor executes an illumination control algorithm to control the intensity of each of the display elements of the electroluminescent display by controlling/adjusting the number of xe2x80x9cskipped cyclesxe2x80x9d in the xe2x80x9ccycle setxe2x80x9d of each waveform applied to a display element to thereby adjust the illumination intensity of the associated element. As described in more detail below, a skip cycle occurs when the first and second electrodes xe2x80x9care in phasexe2x80x9d.
According to one embodiment, a particular display element may have an associated preset number of skipped cycles (e.g., 10 cycles) in a cycle set (e.g., 16 cycles). The processor is able to increase the intensity of the display element by reducing the number of skipped cycles within the cycle set. Conversely, the processor is able to decrease the intensity of the display element by increasing the number of skipped cycles within the cycle set. By adjusting the overall duty cycle of the xe2x80x9ccycle setxe2x80x9d using cycle skipping, the electroluminescent display intensity adjustment is achieved without the limitations and disadvantages of prior art implementations (i.e., voltage adjustment across the entire EL display, base frequency adjustments).
According to the present invention, the cycle skipping method may be used for various applications utilizing intensity adjustments of electroluminescent displays including color compensation, display aging compensation, and display mode operation as described in more detail below. Additionally, selected display channels or elements may be emphasized by increasing the illumination intensity of the selected channels while reducing the illumination intensity of non-selected channels. It will be appreciated by those skilled in the art having the benefit of this disclosure that other applications for adjusting the intensity of an electroluminescent display are equally suitable and are within the scope of the present invention.
The above description sets forth, rather broadly, the more important features of the present invention so that the detailed description of the preferred embodiment that follows may be better understood and contributions of the present invention to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and will form the subject matter of claims. In this respect, before explaining at least one preferred embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and to the arrangement of the components set forth in the following description or as illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.